What is it?

Longitudinal melanonychia describes brown to black streaks/bands that run longitudinally in the nail. It may be present in just one nail or may affect multiple nails. A single nail may have multiple streaks. It is often a source of concern for patients and physicians due to the possibility of melanoma.

What causes it?

Longitudinal melanonychia can occur due to numerous causes. If multiple nails are involved, this is suggestive of normal physiologic pigmentation (commonly occurs in darker-skinned individuals). Trauma, endocrine diseases, nutritional deficiency or drug/pregnancy-induced pigmentation can also lead to multiple bands of melanonychia. If only one nail is involved the differential is more limited and suggests presence of a melanocytic lesion. In children, these are usually benign lentigo or nevi, but new melanonychia in adults raises concern for melanoma. Features concerning for nail melanoma include width of >3mm, extension of the pigment onto the cuticle/proximal nail fold (Hutchinson sign), blurry or irregular borders, nail dystrophy (distortion of the normal nail structures), and triangular shape of band suggesting growth of the lesion; however, in children even benign lesions can share some of these features.

How is it managed?

The management addresses any underlying cause that is identified. In many cases, this simply involves reassurance that the pigmentation is a normal change. If there is concern about a melanoma of the nail, a biopsy of the nail matrix should only be undertaken.  Due to risk of permanent nail dystrophy and rarity of nail melanoma in children, it is typically recommended that pediatric lesions be monitored, and biopsy only performed if they undergo rapid expansion and/or darkening. In adults, however, new isolated melanonychia generally warrants biopsy.